If you’re planning to be here four billion years from now you’ll see an amazing slow-motion sky show when two galaxies collide — Andromeda and our own Milky Way.
What will the sky look like when that happens? (very amazing!)
Will it be dangerous for Earth? (probably not)
How many years before this happens?
Billions and billions.
(video posted in June 2012 by SpaceRip on YouTube)
Billions of years is hard for us humans to really comprehend. Our lives in comparison are a brief moment in time. If I understand the video, the process of the two galaxies merging will also take billions of years to complete. So if humans still exist then, and even if we manage to live somewhat longer lives by then, even over say one hundred years, I imagine the process will look pretty static to most of us. As we personally only get to experience a tiny part of the event over a relatively small amount of time.